In an internal combustion engine with a supercharger, the intake pressure can be higher than the exhaust pressure. Therefore, in the valve overlap state where both the intake valve and the exhaust value are open, fresh air flowing into the combustion chamber can blow by into the exhaust side through the exhaust valve. The appropriate engine control specifications to improve the fuel consumption and emissions of the internal combustion engine with a supercharger vary with the presence or absence of blow-by of fresh air. Therefore, to optimize engine control, it is desirable to detect the presence or absence of blow-by of fresh air with high precision.
JP-A-2008-75549 discloses a system that calculates an internal EGR scavenging amount based on the intake gas pressure, the exhaust gas pressure, the engine speed and the state of control of the variable valve mechanism of the intake valve, determines the presence or absence of blow-by based on the internal EGR scavenging amount, and performs control to reduce the valve overlap period if it is determined that blow-by occurs.
Furthermore, JP-A-63-297746 discloses a system that previously determines the amount of intake gas blowing by into the exhaust side by experiment, stores, in the control unit, a map that represents the intake gas amount as a function of the engine speed and the engine load, and calculates the amount of intake gas blowing by into the exhaust side based on the map. In the case where blow-by of the intake gas occurs, the system calculates the injection fuel amount based on a value obtained by subtracting the amount of intake gas blowing by into the exhaust side from the intake air amount detected by the air flow meter.